NEET-PG 2015 - Microbiology Practice Questions

Q: Which microorganism is the most common cause of pyogenic osteomyelitis?

S. aureus. ***Staph aureus*** - **_Staphylococcus aureus_** is the most frequent cause of **pyogenic osteomyelitis** across all age groups and routes of infection. - Its ability to adhere to bone, form biofilms, and produce toxins contributes to its prevalence in bone infections. *Streptococcus spp.* - While various **_Streptococcus_** species can cause infections, they are less common causes of pyogenic osteomyelitis compared to **_Staphylococcus aureus_**. - **Group A _Streptococcus_** can cause severe invasive infections but rarely involves primary bone infection. *Corynebacterium spp.* - **_Corynebacterium_** species, particularly **_Corynebacterium striatum_**, are increasingly recognized as opportunistic pathogens, especially in immunocompromised individuals or those with foreign bodies. - However, they are not the most common cause of osteomyelitis in the general population. *Neisseria gonorrhoeae (gonococcus)* - **_Neisseria gonorrhoeae_** can cause **disseminated gonococcal infection (DGI)**, which may include joint involvement (**septic arthritis**). - While it can lead to bone pain and swelling, it primarily affects joints and is a less common cause of direct **pyogenic osteomyelitis** than **_S. aureus_**.

Q: Which condition is associated with Streptococcus bovis infection?

Colorectal cancer. ***Colorectal cancer*** - *Streptococcus gallolyticus* (formerly known as *Streptococcus bovis* biotype I) infection, particularly **bacteremia** or **endocarditis**, has a strong association with underlying **colorectal cancer**. - It is hypothesized that the bacteria may play a role in **tumorigenesis** or that the cancerous lesions provide an entry point for the bacteria into the bloodstream. *Chronic lymphocytic leukemia (CLL)* - While patients with CLL are **immunocompromised** and prone to infections, there is no specific association between *Streptococcus bovis* and CLL. - Infections in CLL patients are typically due to encapsulated bacteria, such as *Streptococcus pneumoniae* or *Haemophilus influenzae*. *Hairy cell leukemia (HCL)* - Patients with HCL often experience **immunosuppression** due to neutropenia and monocytopenia, leading to increased susceptibility to infections. - However, there is no direct or specific link between *Streptococcus bovis* infection and HCL itself. *Multiple myeloma (MM)* - Patients with multiple myeloma have **impaired humoral immunity** and are at risk for infections, especially from encapsulated bacteria. - There is no established specific association between *Streptococcus bovis* infection and multiple myeloma.

Q: Which test is used to diagnose congenital syphilis in a newborn born to a syphilitic mother?

Detection of IgM. ***Detection of IgM*** - The presence of **IgM antibodies** in a newborn suggests active infection because maternal IgM does not cross the placenta. - This indicates the newborn's immune system has produced its own antibodies in response to *Treponema pallidum* infection. *Detection of IgG* - **Maternal IgG antibodies can cross the placenta**, so detecting IgG in a newborn does not differentiate between passive transfer from the mother and active newborn infection. - While total IgG might be elevated due to infection, specific IgM is a more reliable indicator of active congenital syphilis. *ZN staining* - **Ziehl-Neelsen (ZN) staining** is used to identify **acid-fast bacteria**, such as *Mycobacterium tuberculosis*, not spirochetes like *Treponema pallidum*. - *Treponema pallidum* is typically visualized using darkfield microscopy or silver stains due to its thin, helical shape. *FTA-ABS test* - The **Fluorescent Treponemal Antibody Absorption (FTA-ABS)** test detects specific antibodies against *Treponema pallidum* but primarily measures IgG, which can be maternally transferred. - While it confirms exposure, an IgM-specific FTA-ABS would be more definitive for congenital syphilis, but the general FTA-ABS test alone is not sufficient to diagnose active infection in a newborn.

Q: Neutralization test is

Nagler reaction. ***Nagler reaction*** - The **Nagler reaction** is a biochemical test used to identify **Clostridium perfringens**, based on its ability to produce **alpha-toxin (lecithinase)**, which hydrolyzes lecithin in egg yolk agar. - It is a neutralization test because the lecithinase activity can be **inhibited (neutralized)** by antitoxin, leading to a diminished zone of opalescence or turbidity around colonies grown on egg yolk agar. *Widal test* - The **Widal test** is an **agglutination test** used to diagnose **typhoid fever** by detecting antibodies against *Salmonella typhi* O and H antigens in a patient's serum. - It measures the presence of antibodies that cause bacterial clumping, not the neutralization of a toxin. *Weil-Felix test* - The **Weil-Felix test** is an **agglutination test** used to diagnose **rickettsial infections** like epidemic typhus, scrub typhus, and Rocky Mountain spotted fever. - It detects antibodies that cross-react with specific **Proteus vulgaris** antigens, and is not a neutralization assay for toxins or enzymes. *Paul Bunnel test* - The **Paul-Bunnell test** is an **agglutination test** used to diagnose **infectious mononucleosis** by detecting heterophile antibodies that agglutinate sheep red blood cells. - It relies on the clumping of red blood cells by antibodies and does not involve the neutralization of a microbial product.

Q: Vital staining technique is used to demonstrate:

Living bacteria. ***Living bacteria*** - **Vital staining** uses dyes taken up by living cells without killing them, allowing for the observation of their morphology and some physiological activities without fixation. - Examples include methylene blue and neutral red, which can stain living cells like bacteria and protozoa, helping to differentiate them from non-living matter or dead cells. *Bacterial toxins* - **Bacterial toxins** are substances produced by bacteria that can harm a host and are typically detected using immunological assays or biological functional tests, not vital staining. - Vital staining focuses on the cellular components and viability of the bacteria themselves, not on secreted products like toxins. *Dead bacteria* - **Dead bacteria** often have compromised cell membranes and would either not take up vital stains in the same way as living bacteria or might take up certain stains (like trypan blue or propidium iodide) that are specifically used to identify dead cells by penetrating their damaged membranes. - Vital staining's primary purpose is to visualize *living* structures, relying on intact cell membranes and metabolic activity. *Fungal spores* - While some **fungal spores** can be stained with various techniques, vital staining methods are generally employed to distinguish living, metabolically active cells (including some fungal cells) from dead ones or debris. - However, the question specifically refers to "vital staining technique" in general terms, and the most classic and direct association is with the demonstration of living microbial cells, especially bacteria.

Q: Commonest cause of nosocomial infection is

Staphylococci. ***Staphylococci*** - **Staphylococci**, particularly *Staphylococcus aureus* (including MRSA) and coagulase-negative staphylococci, are the **most common cause** of nosocomial infections according to current surveillance data from CDC, WHO, and Indian hospital studies. - They are the leading cause of **surgical site infections**, **catheter-related bloodstream infections**, **ventilator-associated pneumonia**, and **skin and soft tissue infections** in hospital settings. - Their ability to form biofilms on medical devices, antibiotic resistance (especially MRSA), and widespread colonization of healthcare workers and patients make them the predominant nosocomial pathogen. *Enterobacteriaceae* - The family **Enterobacteriaceae** (including *E. coli*, *Klebsiella*, *Enterobacter*) represents a major group of gram-negative nosocomial pathogens. - They are very common causes of **urinary tract infections**, **pneumonia**, and **bloodstream infections**, particularly associated with indwelling catheters and ventilators. - While collectively representing a large proportion of nosocomial infections, they are the **second most common** group after Staphylococci in most contemporary studies. *Pseudomonas* - *Pseudomonas aeruginosa* is an important nosocomial pathogen, particularly in **ventilator-associated pneumonia**, **burn infections**, and infections in immunocompromised patients. - It accounts for approximately 10-15% of nosocomial infections and is especially problematic due to its intrinsic antibiotic resistance. *Klebsiella* - **Klebsiella** (particularly *K. pneumoniae*) is a member of the Enterobacteriaceae family and an important individual pathogen causing **pneumonia** and **urinary tract infections** in healthcare settings. - While a common pathogen, it represents only a subset of both the Enterobacteriaceae family and overall nosocomial infections, making it less common than the entire Staphylococci group.

Q: Causative agents of "Vincent's angina"

Borrelia vincenti and Fusobacterium nucleatum. ***Borrelia vincenti and Fusobacterium nucleatum*** - **Vincent's angina**, also known as **acute necrotizing ulcerative gingivitis (ANUG)**, is polymicrobial and characteristically involves a synergistic infection of **spirochetes** (like *Borrelia vincenti*, now classified as *Treponema vincentii*) and **fusobacteria** (like *Fusobacterium nucleatum*). - These organisms thrive in an anaerobic environment, leading to the characteristic ulcerative and necrotic lesions of the gingiva and oral mucosa. - This synergistic infection produces the classic "fusospirochaetal" complex seen on microscopy. *Borrelia burgdorferi and Lactobacillus* - *Borrelia burgdorferi* is the causative agent of **Lyme disease**, a tick-borne illness causing systemic symptoms, not Vincent's angina. - *Lactobacillus* species are common commensal bacteria found in the oral cavity, gut, and vagina, and are not pathogenic in the context of Vincent's angina. *Leptospira and Treponema pallidum* - *Leptospira* species cause **leptospirosis**, a zoonotic disease with symptoms like fever, headache, and muscle aches, often affecting the kidneys and liver. - *Treponema pallidum* is the causative agent of **syphilis**, a sexually transmitted infection, which presents with different oral lesions (e.g., chancre, mucous patches) that are distinct from Vincent's angina. *Borrelia recurrentis and Bacteroides* - *Borrelia recurrentis* causes **relapsing fever**, characterized by recurrent episodes of fever and other systemic symptoms, transmitted by lice or ticks. - While *Bacteroides* are common anaerobic bacteria in the oral flora, they are not the primary synergistic pair specifically associated with the distinct clinical presentation of Vincent's angina, as are the spirochetes and fusobacteria.

Q: All the following are common nosocomial infections except:

Mycobacterium. ***Mycobacterium*** - **Mycobacterium** species are not typically considered common causes of **acute nosocomial infections** because they are slow-growing and usually cause chronic infections. - While healthcare workers or patients can acquire tuberculosis in healthcare settings, it is less common for *Mycobacterium* to be the cause of rapidly developing, typical healthcare-associated infections like pneumonia or bloodstream infections. *Staph. aureus* - **_Staphylococcus aureus_** is a very common cause of **nosocomial infections**, particularly **MRSA (methicillin-resistant *S. aureus*)**, leading to surgical site infections, bloodstream infections, and pneumonia. - It colonizes healthcare workers and patients, making it easily transmissible in hospital environments. *Enterobacteriaceae* - **Enterobacteriaceae** (e.g., _E. coli_, _Klebsiella_, _Enterobacter_) are frequently implicated in **nosocomial infections**, especially **urinary tract infections (UTIs)**, pneumonia, and bloodstream infections. - These bacteria are part of the normal flora but can cause serious infections when introduced into sterile sites or in immunocompromised patients. *P. aeruginosa* - **_Pseudomonas aeruginosa_** is a significant cause of **nosocomial infections**, particularly in intensive care units (ICUs) and among immunocompromised patients. - It is known for causing **ventilator-associated pneumonia (VAP)**, UTIs, and wound infections, often exhibiting multidrug resistance.

Q: Hebra nose is caused by:

Frisch bacillus. ***Frisch bacillus*** - **Frisch bacillus**, also known as *Klebsiella rhinoscleromatis*, is the causative agent of **rhinoscleroma**, which often presents as a condition causing tumor-like growths in the nose, leading to the characteristic "Hebra nose." - **Hebra nose** refers to the chronic, deforming nasal lesion associated with late stages of **rhinoscleroma**, characterized by hardening and widening of the nose. *C. diphtheriae* - *Corynebacterium diphtheriae* causes **diphtheria**, primarily affecting the respiratory tract and skin. - It forms a **pseudomembrane** in the throat and can lead to systemic complications due to toxin production, but it does not cause Hebra nose. *Pseudomonas* - *Pseudomonas aeruginosa* is an opportunistic pathogen commonly causing **nosocomial infections**, such as pneumonia, urinary tract infections, and wound infections. - While it can cause various infections, it is not associated with the specific nasal deformity known as Hebra nose. *Staph aureus* - *Staphylococcus aureus* is a common bacterium causing a wide range of infections, including **skin infections** (e.g., boils, cellulitis), **pneumonia**, and **sepsis**. - Although it can cause nasal colonization and local infections, it does not cause the chronic, deforming condition known as Hebra nose.

Q: Not true about gas gangrene:

Cl perfringens produce heat-labile spores. ***Cl perfringens produce heat-labile spores*** - *Clostridium perfringens* spores are, in fact, **heat-resistant**, allowing them to survive harsh conditions and subsequently germinate into vegetative cells causing infection. - This heat resistance is a crucial factor in food poisoning outbreaks and wound infections, as spores can survive cooking temperatures. *Metronidazole is the drug of choice* - While metronidazole can be used as an adjunct, **penicillin G** is generally the primary antibiotic of choice for gas gangrene, often in combination with other agents like clindamycin. - **Surgical debridement** and **hyperbaric oxygen therapy** are also critical components of treatment, as antibiotics alone are often insufficient. *Most common cause is Cl perfringens* - **_Clostridium perfringens_** is indeed the most frequent cause of gas gangrene (clostridial myonecrosis), accounting for approximately 80-95% of cases. - This bacterium produces potent **exotoxins** that cause rapid tissue destruction and gas formation, leading to the characteristic symptoms. *Extensive necrosis of muscles* - Gas gangrene is characterized by **rapid and extensive necrosis of muscle tissue**, which is caused by the potent toxins produced by clostridial species, particularly alpha-toxin. - This muscle destruction leads to systemic toxicity, pain, and the production of gas within the tissues.

Question 1

Which microorganism is the most common cause of pyogenic osteomyelitis?

Accepted Answer

S. aureus

Answer

Streptococcus spp.

Answer

Corynebacterium spp.

Answer

Neisseria gonorrhoeae (gonococcus)

Question 2

Which condition is associated with Streptococcus bovis infection?

Accepted Answer

Colorectal cancer

Answer

Chronic lymphocytic leukemia (CLL)

Answer

Hairy cell leukemia (HCL)

Answer

Multiple myeloma (MM)

Question 3

Which test is used to diagnose congenital syphilis in a newborn born to a syphilitic mother?

Accepted Answer

Detection of IgM

Answer

Detection of IgG

Answer

ZN staining

Answer

FTA-ABS test

Question 4

Neutralization test is

Accepted Answer

Nagler reaction

Answer

Widal test

Answer

Weil-Felix test

Answer

Paul-Bunnell test

Question 5

Vital staining technique is used to demonstrate:

Accepted Answer

Living bacteria

Answer

Bacterial toxins

Answer

Dead bacteria

Answer

Fungal spores

Question 6

Commonest cause of nosocomial infection is

Accepted Answer

Staphylococci

Answer

Klebsiella

Answer

Enterobacteriaceae

Answer

Pseudomonas

Question 7

Causative agents of "Vincent's angina"

Accepted Answer

Borrelia vincenti and Fusobacterium nucleatum

Answer

Borrelia burgdorferi and Lactobacillus

Answer

Leptospira and Treponema pallidum

Answer

Borrelia recurrentis and Bacteroides

Question 8

All the following are common nosocomial infections except:

Accepted Answer

Mycobacterium

Answer

Staph. aureus

Answer

Enterobacteriaceae

Answer

P. aeruginosa

Question 9

Hebra nose is caused by:

Accepted Answer

Frisch bacillus

Answer

C. diphtheriae

Answer

Pseudomonas

Answer

Staph aureus

Question 10

Not true about gas gangrene:

Accepted Answer

Cl perfringens produce heat-labile spores

Answer

Metronidazole is the drug of choice

Answer

Most common cause is Cl perfringens

Answer

Extensive necrosis of muscles

NEET-PG 2015 — Microbiology